The invention relates to health care and sports, particularly to applications which aim to determine variables relating to human energy metabolism and/or glucose content in a human body.
The human energy economics mainly comprises carbohydrates, fats and proteins. How these are used and proportioned depends on bodily condition, the amount of nutrients in use and the intensity of exercise to be performed. The bodily condition can be studied e.g. through activity, temperature and blood pressure. The exercise stress intensity, in turn, can be measured e.g. as a heart rate frequency with respect to time, which gives a temporary, rough estimate of the exercise stress. In connection with various diseases, such as diabetes, it is important to determine the bodily energy balance and glucose content in order to find suitable treatment. Furthermore, the effect of exercise stress level in athletes on the energy balance and energy metabolism is important as regards planning a suitable diet.
The known methods for determining energy metabolism levels are based on measuring the heart rate during an exercise. Energy consumption has been estimated e.g. by an equation according to Formula (1):
EE=a+b*HR, whereinxe2x80x83xe2x80x83(1)
EE describes the level of energy consumption, a and b are constants by which the linear dependency between heart rate HR and EE is determined. The known method has serious disadvantages. Energy consumption calculated by the method according to Formula (1) does not take any previous cumulative exercise stress nor the quality thereof into account. The linear model is used because the energy consumption measurements being currently used are mainly based on laboratory measurements during ascending exercise stress or using constant exercise stress at a certain work load.
An object of the invention is to provide an improved method for determining human energy metabolism. A further object of the invention is to provide an improved method for estimating a glucose content in a human body. This is achieved by a method disclosed in the following. The method is a method for measuring human energy metabolism, in which method information on a person""s heart rate is measured in the form of one or more heart rate parameters. The method comprises forming, by means of a mathematical model modelling human metabolism, the person""s energy metabolism level as an output parameter of the model using as input parameters of the model said one or more heart rate parameters and one or more physiological parameters each describing a physiological characteristic of the person, and using the output parameter of the model for estimating the person""s energy metabolism.
The invention also relates to a method for measuring the amount of glucose in a human body, in which method information on a person""s heart rate is measured in the form of one or more heart rate parameters. The method comprises supplying one or more heart rate parameters and one or more physiological parameters describing a physiological characteristic of the person as input parameters into a mathematical model modelling human glucose consumption, by means of which input parameters one or more of the following are formed as an output parameter of the model: the person""s glucose content level, amount of glucose left in the person""s body, which said one or more output parameters are used for estimating the amount of glucose used and/or the amount of glucose left in the body.
The invention also relates to a heart rate measurement arrangement comprising a calculating unit comprising a mathematical model arranged to form a person""s energy metabolism level as an output parameter of the model using as input parameters of the model one or more heart rate parameters and one or more physiological parameters each describing a physiological characteristic of the person, the heart rate measurement arrangement further comprising display means for displaying information formed in the calculating unit.
The invention also relates to a heart rate measurement arrangement comprising a calculating unit comprising a mathematical model arranged to form, using as input parameters of the model one or more heart rate parameters and one or more physiological parameters each describing a physiological characteristic of a person, one or more of the following as an output parameter of the model: the person""s glucose content level, amount of glucose left in the person""s body, which heart rate measurement arrangement further comprises display means for displaying information formed in the calculating unit.
Preferred embodiments of the invention are disclosed in the dependent claims.
The invention thus relates to a method and apparatus for measuring human energy metabolism. The method of the invention is preferably implemented by a mathematical model which is based on the physiological facts of the human energy metabolism. In connection with the description of the invention, a mathematical model refers to a set of mathematical procedures and rules that are employed to form output parameter values from input parameter values. The mathematical procedures include arithmetic operations, such as adding, subtracting and multiplying. The mathematical model may of course also be implemented as a table or a database, in which case an output parameter value corresponding to a particular input parameter is read directly from the database. In an embodiment of the invention, the level of energy metabolism, i.e. the amount of energy consumed, is given as output variables of the mathematical model. Energy consumption can be determined as energy/time unit, i.e. kcal/min. In a preferred embodiment of the invention, the quality of energy metabolism, which means that the energy used is divided into different forms of energy, such as carbohydrates, fats and proteins, is given as output parameters of the model. In a preferred embodiment of the invention, the amount of energy left in the body is given as an output variable. In an embodiment, the quality of the remaining energy divided into different energy components is given as an output parameter. More than one output parameter of the output parameters disclosed above may also be simultaneously given as an output parameter of the model.
The mathematical model according to an embodiment of the invention returns as its output parameter one or more of the following: the glucose used by the body or the amount of glucose left in the person""s body.
The set of input parameters of both the model modelling energy metabolism and the model modelling glucose consumption may vary greatly. In the solution of the invention, at least one or more heart rate parameters to be measured from heart rate information are introduced as input parameters into the model. A heart rate parameter may be e.g. heart rate, standard deviation of the heart rate, rate of change of the heart rate or other such variable measurable from heart beats. Furthermore, at least one physiological parameter describing the physiology of the user is introduced as input information into the model. The physiological parameters include height, weight, age and sex. The model can be made more accurate by using one or more optional parameters as input parameters of the model. In a preferred model, the amount of energy supplied to the body is introduced as an input parameter into the model. The amount of supplied energy refers to energy that has been consumed by eating or drinking or administered e.g. through an injection. In a preferred embodiment, the amount of energy supplied to the body can be divided into carbohydrates, fats and proteins according to the energy quality. An optional input parameter is body temperature, which can be measured e.g. from the skin by a thermometer. Furthermore, an optional input parameter of the model is the surrounding temperature, which affects the metabolism level in the same way as the body""s own temperature, i.e. the higher the temperature, the higher the metabolism level. The model may also use a person""s blood pressure as an input parameter, the blood pressure affecting the metabolism such that high blood pressure corresponds with high metabolism level. In a preferred embodiment, the model uses the amounts of respiratory gases, i.e. oxygen and carbon dioxide, as optional input parameters.
In a preferred embodiment of the invention, the above-described mathematical model is implemented as a neural network. In a neural network, the effect of each input parameter on each output parameter is found out by finding out the weighting coefficient describing the effect. The model is preferably trained by a sufficiently large amount of user data to enable the model to conclude the effect of each input parameter on each output parameter. The set of users used in the training is preferably very large, i.e. it comprises a group of hundreds or even thousands of people having physiological characteristics that provide as comprehensive a sample as possible. By supplying a user""s physiological parameters into the trained neural network quite a good classification of the user in the model can be achieved. In a preferred embodiment, the results given by the model are improved by a reference exercise. The reference exercise is carried out at a known exercise stress level, enabling the exact values of some input parameters, such as the respiratory gases, to be measured. The operation of the neural network can be further improved by introducing feedback into the model, whereby the model can be further improved by utilizing the measurement results obtained.
In a solution according to a preferred embodiment of the invention, in order to measure energy metabolism and/or glucose, a person whose energy levels are to be monitored uses a heart rate monitor. A heart rate monitor is a device used in sports and medicine to measure information on a person""s heart rate either from an electric impulse transmitted by the heart or from the pressure caused by a heart beat on an arterial vessel. Heart rate monitors are known e.g. to comprise an electrode belt to be arranged on a user""s chest to measure the heart rate by means of two or more electrodes. The electrode belt transmits the measured heart rate information inductively as one or more magnetic pulses per heart beat e.g. to a receiver unit worn on the wrist. On account of the received magnetic pulses, the receiver unit calculates the heart rate and, if necessary, other heart rate variables, such as the moving standard deviation of the heart rate. The receiver unit, i.e. the wrist monitor, often also comprises a display for displaying heart rate information to the performer of an exercise, and an interface for the other facilities of the heart rate monitor. In the above-described situation, a heart rate monitor refers to an integrated whole comprising an electrode belt and a receiver unit. The heart rate monitor may also consist of one part only such that the display means are also located on the chest, which means that no information needs to be transmitted to a separate receiver unit. Furthermore, the heart rate monitor may consist of a mere wrist monitor to be arranged on the wrist, operating without an electrode belt arranged on the chest and measuring the heart rate information from the pressure in the vessel. In connection with the description of the invention, a heart rate measurement arrangement refers to the heart rate monitor solutions described above. The heart rate measurement arrangement also comprises solutions wherein the heart rate information is transmitted to an external computer or to an information network comprising display means, such as a display of a computer, for displaying the information measured or formed by the heart rate monitor.
The mathematical model required by the method of the invention and the other facilities required by the models are preferably implemented by software using a processor of the heart rate monitor. The models and facilities may also be implemented as ASIC, using separate logic components or the like. In a preferred embodiment of the invention, the heart rate monitor comprises supply means for supplying input parameter values, which supply means may be e.g. a keypad of the heart rate monitor, display equipment supporting the control, speech control, telecommunication gate for external control or the like. The heart rate monitor preferably also comprises display means for displaying output parameters. The output parameters may of course be transmitted to the user in other ways as well, e.g. by means of a speech controller or a telecommunication connection.
In connection with the description of the invention, a fitness exercise, or an athletic exercise, refers to a physical exercise wherein a person""s heart rate level for a given time, e.g. for more than 10 minutes, exceeds a heart rate level corresponding to a rest state. An exercise may be considered to be divided e.g. into the following phases: warm-up phase, active phase and recovery phase, the exercise being preceded and followed by a state of rest. The different phases may be determined and separated e.g. on account of heart rate levels and/or exercise stress levels. A recovery phase, for instance, can then be determined as a performance level on which the heart rate level is dropped from 130 beats/minute to a rest level of 70 beats/minute. The invention is not restricted to measuring during an exercise only but the present invention is well suited to measuring during a rest state as well.
The invention provides several advantages. In comparison to the known methods, a person""s bodily condition can be followed much more accurately as regards the energy metabolism and/or glucose parameters. Indirectly, this means that the energy balance in athletes and persons suffering from certain diseases can be monitored more accurately than in the known methods. Furthermore, when in use, the method and apparatus of the invention provide a non-invasive way of estimating the energy metabolism and/or amount of glucose in a body.